(1) Field of the Invention
This invention relates to an SDH (Synchronous Digital Hierarchy) transmission system, an SDH transmission equipment and a line switching control method in the SDH transmission system which can be favorably used for making the line configuration of the SDH transmission system redundant.
(2) Description of the Related Art
Recently, an introduction of so called SDH network [called SONET (Synchronous Optical NETwork) in North America]) has been planned in every countries in the world along with the standardization of the transmission technique or method of SDH network recommended by ITU-T (while the SONET is recommended by Bellcore). This SDH network (SDH transmission system) is constructed by using various transmission equipment in accordance with SDH transmission system such as line terminal equipment or regenerator (hereinafter called xe2x80x9cSDH transmission equipmentxe2x80x9d or xe2x80x9cSDH equipmentxe2x80x9d).
As shown in FIG. 9, for example, the SDH transmission system 100 usually makes the line which connects an SDH equipment 200 with an SDH equipment 300 have a redundant configuration for enhancing the reliability of communication by providing a protection line 500 besides a work line 400 and once a fault such as a disconnection of line occurs on the work line 400, the communication line is readily switched to the protection line 500 so as to avoid the disconnection of communication (main signal) caused by the line fault.
In the SDH network, the switching between the above-mentioned work line 400 and the protection line 500 is controlled with APS (Automatic Protection System) byte (K1, K byte) defined in a section overhead (SOH) 11 of a transmission frame [STM: Synchronous Transfer Module (STS: Synchronous Transport Signal in SONET)] having a frame format as shown in FIG. 11, for example.
In FIG. 11, a portion which follows SOH 11 is called as payload 12 and in this payload 12, a given number [e.g. 3 for VC-3 (approximately 51 Mb/s) and 1 for VC-4 (approximately 150 Mb/s)] of desired communication data (main signal) such as ATM (Asynchronous Transfer Mode) cells are stored as lower order virtual containers (VC) corresponding to its transmission speed and their stored locations [the head (J1 byte) of the path overhead (POH) 13] are indicated by AU pointers 14 of SOH 11.
For realizing the above-mentioned APS control function, the SDH equipment 200 (300), as shown in FIG. 10, for example, at least comprises a work unit 201W (301W) which performs a transmission processing (bidirectional) through the work line 400 (a down-line 400A, an up-line 400B) and a protection unit 201P (301P) which functions as a backup for this work line 201W(301W) and performs a transmission processing (bidirectional) through the protection line 500 (a down-line 500A, an up-line 500B). The SDH equipment 200 (300) further includes an APS control firmware 202(302) which performs a switching (APS) control between these units 201W, 201P (301W, 301P).
In this case, however, the same signals (transmission frames) are transmitted through the work down-line 400A (or the up-line 400B) and the protection down-line 500A (or the up-line 500B) respectively and, in an usual operation, the reception terminal (SDH equipment 200, 300) selectively receives either one of signals (e.g. the signal having a better quality).
In FIG. 10, numerals 203 (303) indicate main signal transmission parts, numerals 204(304) indicate POH insertion processing parts for inserting POH 13 into the transmitting main signals, numerals 205(305) indicate POH termination processing parts which terminate POH 13 of the main signals after a termination of SOH 11, and numeral 206 (306) indicate main signal reception parts for receiving main signals after termination of POH 13.
In FIG. 10, numerals 600, 700 respectively indicate microcomputers (xcexc-COM). Using these microcomputers 600, 700, a maintenance man of the network individually sets setting information on APS control such as a unidirectional/bidirectional switching operation, a 1+1/1+N switching operation to respective APS control firmware (hereinafter simply referred to as xe2x80x9cfirmwarexe2x80x9d) 202, 302.
Here, xe2x80x9cthe unidirectional switching operationxe2x80x9d means, for example, an operation to switch both work down-line 400A and work up-line 400B to the protection down-line 500A and the protection up-line 500B when a fault occurs on the work down-line 400A, while xe2x80x9cthe bidirectional switching operationxe2x80x9d means, for example, an operation to switch only the down-line 400A to the protection down-line 500A when a fault occurs on the down-line 400A.
The xe2x80x9c1+1 switching operationxe2x80x9d means a switching operation used when the protection line is configured such that one protection line corresponds to one work line, while the xe2x80x9c1+N switching operationxe2x80x9d means a switching operation used when the protection line is configured such that one protection line corresponds to a plurality (N: integers more than 2) of work lines. In the configuration shown in FIG. 10, since the work units 201W and 301W (the protection units 201P and 301P) respectively include the down-line 400A (500A) and the up-line 400B (500B), the APS setting information to be set to the firmwares 202 and 302 become the xe2x80x9c1+1 switching operationxe2x80x9d and the xe2x80x9cunidirectional switching operationxe2x80x9d.
Incidentally, as shown in FIG. 10, the work unit 201W (301W) is provided with a line fault detection/SOH termination part 211W (311W), a high impedance part (switching part) 212 W (312W) and an SOH insert processing part 213W (313W), while the protection unit 201P (301P) is provided with a line fault detection/SOH termination part 211P (311P), a high impedance part (switching part) 212P (312P) and an SOH insert processing part 213P (313P).
Here, the SOH insert processing parts 213W, 213P (313W, 313P) respectively build up their transmission frames (synchronous transfer modules) by giving (inserting) the SOH 11 to the main signals addressed to the opposite side equipment 300 (200) in which the POH is already inserted. During this insert processing of the SOH 11, xe2x80x9cthe switching requestxe2x80x9d and the xe2x80x9cswitching responsexe2x80x9d generated in the firmware 202 (302) are inserted and transmitted to the opposite side equipment 300 (200) as the APS byte (K1, K byte) of the SOH 11.
The line fault detection/SOH termination parts (hereinafter simply referred to as the xe2x80x9ctermination partsxe2x80x9d) 211W, 311W (211P, 311P) respectively detect a fault of the work line 400 (the protection line 500) by monitoring fault factors such as an input disconnection of optical signals (transmission frame) or the deterioration of input optical signals with an application (software) during the communication operation using the work units 201W, 301W (the protection units 201P, 301P), while the termination parts 211W, 311W (211P, 311P) detect the xe2x80x9cswitching requestxe2x80x9d or the xe2x80x9cswitching responsexe2x80x9d from the opposite side equipment 300 (200) which are inserted to the SOH 11 as the APS byte by terminating the SOH 11 of the reception-side transmission frame.
Furthermore, when the line fault is detected at the termination part 211W(311W) or 211P (311P), the firmware 202 (302) recognizes the content of the fault and performs the transmission and reception of the APS byte between the opposite side equipment 300 (200) through the protection line 500 (or the work line 400) and performs the switching control between the work unit 201W (301W) and the protection unit 201P (301P) of the own side equipment.
The above switching control is performed in such a manner that the firmware 202 (302) controls the conducting state and nonconducting state of the switching parts 212W, 212P (312W, 312P) and such a control is always performed in response to the APS setting information set by the microcomputer 600 (700).
Hereinafter, the APS control performed in the SDH transmission system 100 (the SDH transmission equipment 200, 300) is explained in view of a case that a fault occurs on the down-line 400B of the work line 400.
When the fault occurs on the down-line 400B, this fault is detected at the termination part 211W of the work unit 201W of the reception-side SDH equipment 200. Then, the firmware 202 generates xe2x80x9ca switching requestxe2x80x9d addressed to the opposite side station 300 in accordance with the APS setting information set by the microcomputer 600 in advance. This xe2x80x9cswitching requestxe2x80x9d is inserted to the SOH 11 of the transmission frame as APS byte (K1 byte) at the SOH insert processing part 213P of the protection unit 201P and is transmitted to the opposite side equipment 300 through the protection up-line 500B.
In the opposite side equipment 300, when the APS byte is detected at the termination part 311P of the protection unit 301P, the firmware 302 switches the system in service from the work unit 301W to the protection unit 301P in accordance with the APS setting information set by the microcomputer 700 in advance. Upon completion of this switching, the xe2x80x9cswitching responsexe2x80x9d addressed to the opposite side equipment 200 is generated. This xe2x80x9cswitching responsexe2x80x9d is inserted into the SOH 11 of the transmission frame for download as the APS byte (K 2 byte) and is transmitted through the protection down-line 500A.
When the APS byte is detected at the termination part 211P of the protection unit 201P of the SDH equipment 200, the firmware 202 confirms the completion of the switching of the opposite side equipment 300 and switches the system in service at own side equipment 200 from the work unit 201W to the protection unit 201P in accordance with the APS setting information set by the microcomputer 600 as in the case of the opposite side equipment 300.
Accordingly, the communication performed using the work up-line 400A is relieved by the protection up-line 500A so that a normal communication can be continued. When a line fault is detected at the termination part 311W of the opposite side equipment 300, the firmware 302 performs the similar processing as the starting point. Furthermore, when a line fault is detected in the protection unit 201P or 301P, the transmission and reception of the APS byte are performed through the work unit 201W (301W) in a similar manner so as to provide a switching from the protection unit 201P (301P) to the work unit 201W (301W).
In the above-mentioned SDH transmission system 100 (SDH transmission system 200, 300), however, usually, routes (e.g. paths and sections) are set in a plurality of directions and a plurality of APS setting information which correspond to these routes are present. Accordingly, assuming that setting of the APS setting information to the firmware 202, 302 are independently performed corresponding to respective SDH equipment 200, 300, this setting may be performed erroneously in either one of these SDH equipment 200 (or 300).
In such a case, since the setting at respective firmware 202, 302 are different from each other, the respective SDH equipment 200, 300 perform the switching control different from each other at the time of occurrence of a line fault so that, in a worst case, the main signal suffers from the nonconductive state and the normal line relief cannot be performed.
Conventionally, several techniques have been proposed for solving these problems, wherein one technique which is disclosed in Japanese Patent laid-open No. HEI 7-264156 solves the problem by detecting such a disagreement of setting (a mode mismatch) at the SDH equipment 200 (300) and another technique disclosed in Japanese Patent laid-open No. HEI 8-288981 performs a normal switching operation even when a mode mismatch is present.
These techniques, however, place their focuses on how to cope with the disagreement of setting which have already occurred or will occur in future. In other words, these techniques regard the occurrence of the disagreement of setting as the premise. Accordingly, functions to be added to the SDH equipment are increased, and the equipment configuration becomes large-sized, and the line switching control becomes complicated. In view of the above, these techniques are less than optimal for resolving the above-mentioned disagreement of setting.
The present invention has been made to overcome these problems and it is an object of the present invention to provide an SDH transmission system, an SDH transmission equipment and a line switching control method for an SDH transmission system which prevents the occurrence of the disagreement of setting and always assures a normal line switching control between equipment which face each other.
For achieving the above object, the present invention discloses the SDH transmission system which is provided with at least two SDH transmission equipments which are connected while facing each other through a work line which transmits a transmission frame conforming to the SDH transmission method and a protection line which functions as a backup for the work line, wherein one SDH transmission equipment comprises a first line switching control part which performs a line switching control between the work line and the protection line in accordance with setting information on the line switching control and a setting information transfer part which transfers the setting information to other SDH transmission equipment as setting information on a line switching control at other SDH transmission equipment, and other SDH transmission equipment comprises a setting information detection part which detects the setting information transferred from one SDH transmission equipment and a second line switching control part which performs a line switching control at own side in accordance with the setting information detected by the setting information detection part.
Accordingly, with the SDH transmission system of the present invention, setting information on the line switching control between the work line and the protection line in one SDH transmission equipment can be transferred as setting information on other opposite side SDH transmission equipment so that mere setting of setting information at one SDH transmission equipment provides the same setting of setting information at other SDH transmission equipment. With such a provision, following advantages are brought about.
(1) The disagreement of setting information per se at respective SDH transmission equipment can be prevented so that it is no more necessary to perform a special processing for solving the disagreement of setting information at respective SDH transmission equipment and the normal line switching control can be always performed between opposite side equipment.
(2) It is no more necessary to perform a line switching control for a plurality of SDH transmission equipment at respective SDH transmission equipment individually so that a burden incurred by the line switching control setting operation can be drastically reduced.
(3) The setting information on a plurality of SDH transmission equipment can be integrally administrated at one SDH transmission equipment so that the system can extremely easily cope with the alteration of the setting information.
In the above SDH transmission system, the setting information transfer part of one SDH transmission equipment may transfer setting information to other SDH transmission equipment by storing the setting information into the transmission frame and the setting information detection part of other SDH transmission equipment may preferably detects the setting information which is transferred while having been stored in the transmission frame.
In this manner, by transferring the setting information to other SDH transmission equipment while storing information in the transmission frame, the transfer of the setting information can be performed with the SDH transmission system having a simple configuration.
Furthermore, other SDH transmission equipment may preferably be provided with a setting information re-transfer part which transfers the setting information detected by the setting information detection part to an SDH transmission equipment other than the above-mentioned one SDH transmission equipment as setting information on the line switching control of such other SDH transmission equipment.
Accordingly, by merely setting the setting information to the SDH transmission equipment which transfers the setting information, the same setting information is set at a plurality of other SDH transmission equipment so that a burden incurred by a setting operation for the line switching operation can be drastically reduced.
The present invention also discloses an SDH transmission equipment which is connected with other SDH transmission equipment while facing other transmission equipment through a work line which transmits a transmission frame conforming to the SDH transmission method and a protection line which functions as a backup for the work line, wherein setting information on a line switching control between the work line and the protection line is set and the SDH transmission equipment comprises a first line switching control part which performs the line switching control in accordance with the setting information on the line switching control and a setting information transfer part which transfers the setting information to other SDH transmission equipment as setting information on a line switching control at other SDH transmission equipment.
With such a configuration, the SDH transmission equipment can obtain advantages similar to those advantages set forth in the above-mentioned paragraphs (1) to (3).
The setting information transfer part may preferably be configured such that the setting information can be transferred while being stored in the transmission frame. For example, the setting information transfer part may be constructed such that the setting information is stored in a section overhead of the transmission frame. In this case, the setting information may be stored in an undefined portion of the section overhead or in an unused portion of a predefined byte of the section overhead.
When the setting information is stored in the section overhead of the transmission frame, an existing overhead processing in the SDH transmission method can be utilized so that a storing processing of the setting information can be performed with an extremely simple configuration.
When the setting information is stored in the undefined portion of the section overhead, it ensures the reliable transfer of the setting information. Furthermore, when the setting information is stored in the unused portion of the predefined byte of the section overhead, the processing on existing predefined byte can be utilized so that the setting information can be stored with a further simplified configuration.
The setting information transfer part may be constructed such that the setting information is stored in a path overhead of the transmission frame. In this case, the setting information may preferably be stored by using an unused portion of a predefined byte of the path overhead.
Accordingly, even when a detecting portion of the section overhead at the reception side becomes abnormal, it does not affect the detection of the setting information so that the reliability of the transfer of the setting information is enhanced. Furthermore, when the setting information is stored by using an unused portion of a predefined byte of the path overhead, a processing on the existing predefined byte can be utilized so that the storing processing of the setting information can be realized with a simple configuration.
The present invention also discloses the SDH transmission equipment which is connected with a first other SDH transmission equipment while facing the first other SDH transmission equipment through a work line which transmits a transmission frame conforming to the SDH transfer method and a protection line which functions as a backup for the work line, wherein the SDH transmission equipment comprises a setting information detection part which detects setting information on a line switching control between the work line and the protection line at the first other SDH transmission equipment transferred from the first other SDH transmission equipment and a second line switching control part which performs a line switching control at own side in accordance with the setting information detected by the setting information detection part.
With such a configuration, the SDH transmission equipment can obtain advantages similar to those advantages set forth in the above-mentioned paragraphs (1) to (3).
In the above mentioned SDH transmission equipment, the setting information detection part may preferably detects the setting information transferred from the first SDH transmission equipment having been stored in the transmission frame. For example, the setting information detection part may be constructed so as to detect the setting information stored in a section overhead of the transmission frame. In this case, it may be possible to detect the setting information stored in an undefined portion of the section overhead. It may be also possible to detect the setting information stored in an unused portion of a predefined byte of the section overhead.
When the setting information detection part of the SDH equipment detects the setting information while having been stored in the transmission frame, the detection of the setting information can be performed with a simple configuration. Furthermore, when the setting information detection part detects the setting information stored in the section overhead of the transmission frame, an existing overhead processing of the SDH transmission method can be utilized so that the detection processing of the setting information can be performed with an extremely simple configuration.
When the setting information detection part detects the setting information stored in the undefined portion of the section overhead, the setting information detection part can assuredly detect the setting information. Furthermore, when the setting information detection part detects the setting information stored in the unused portion of the predefined byte of the section overhead, an existing predefined byte processing can be utilized so that the detection processing of the setting information can be performed with a further simplified configuration.
Furthermore, the setting information detection part may preferably be constructed such that it can detect the setting information stored in the path overhead of the transmission frame. In this case, it is preferable to detect the setting information stored in an unused portion of a predefined byte of the path overhead.
When the setting information detection part detects the setting information stored in the path overhead of the transmission frame, even when the detecting part for the section overhead becomes abnormal, it does not affect the detection of the setting information so that the setting information can be detected normally. Furthermore, when the setting information detection part detects the setting information stored by using an unused portion of a predefined byte of the path overhead portion, an existing predefined byte processing can be utilized so that the detection processing of the setting information can be performed with a simple configuration.
The SDH transmission equipment may also preferably be provided with a setting information re-transfer part to transfer the setting information detected by the setting detection part to a second SDH transmission equipment other than the first SDH transmission equipment as setting information on a line switching control at the second SDH transmission equipment.
In this case, the setting information re-transfer part may also preferably be constructed such that it can transfer the setting information by storing the setting information into the transmission frame to the second SDH transmission equipment. For example, the setting information may preferably be stored in the section overhead of the transmission frame. In this case, the setting information may be stored in the undefined portion of the section overhead or in the unused portion of the section overhead.
The setting information re-transfer part may preferably be constructed such that the setting information is stored in the path overhead of the transmission frame. In this case, it is also preferable to store the setting information by using an unused portion of a predefined byte of the path overhead.
The present invention also discloses a line switching control method in an SDH transmission system which includes at least two SDH transmission equipments which use a transmission frame conforming to the SDH transmission method and where respective SDH transmission equipments are connected through a work line which transmits the transmission frame and a protection line which functions as a backup for the work line, wherein setting information at one SDH transmission equipment on a switching control between the work line and the protection line is transferred from one SDH transmission equipment to the other SDH transmission equipment and the other SDH transmission equipment performs its own line switching operation in accordance with the setting information transferred from the one SDH transmission equipment.
With such a configuration, the line switching control method in an SDH transmission system can also obtain advantages similar to those advantages set forth in the above-mentioned paragraphs (1) to (3).
In the above line control method, the other SDH transmission equipment may further transfer the setting information to an SDH transmission equipment other than one SDH transmission equipment for a line switching control of this SDH transmission equipment. In this case, the setting information may preferably be transferred by being stored in a transmission frame.
Furthermore, in this case, when the setting information is transferred to the second SDH transmission equipment by being stored in the section overhead (e.g. undefined byte or unused portion of predefined byte) or the path overhead (e.g. an unused portion of predefined byte) of the transmission frame, the previously mentioned operations and advantages are obtained.